1. Field of the Invention
The present invention is generally related to plasma processing and, more particularly, to a method and apparatus for monitoring consumption of a component used in plasma processing.
2. Discussion of the Background
In semiconductor processing tools, certain components within a processing chamber are subjected to processing conditions that eventually cause the components to deteriorate to the extent that they must be replaced. In etch systems, for example, a chuck focus ring surrounds a wafer chuck and is subjected to erosion by the plasma and etch chemistry. After the thickness of the focus ring is reduced to a predetermined percentage of its original thickness or to a predetermined minimum thickness, the focus ring is replaced with a new one. Other examples of consumable components include inject plates, electrodes in capacitive coupled plasma reactors, chamber liners and deposition shields, and consumable parts in batch furnaces.
In practice, it is difficult to determine exactly when a consumable component must be replaced. For the sake of efficiency, a processing tool can not be taken offline after every individual tool process for the purpose of opening the processing chamber and measuring the remaining size of a consumable component. Also, a single processing tool may perform various processes using the same consumable component, and each process condition may cause the consumable component to erode at a different rate. Thus, it is difficult to predict with certainty the deterioration of a consumable component based on an elapsed usage time.
One replacement scheduling method involves corresponding a particular consumable component to a number of wafer starts; that is, the component is replaced after a certain predetermined number of wafer starts has occurred. However, this approach is cost efficient only if the tool in question is used to run the same processes on all wafer batches. In a system in which the tool is used to run different processes on different batches of wafers, such as in foundry integrated chip manufacturing plants, the wafer-start method can result in a waste of consumable part lifetime. For example, using this approach, a consumable component may be replaced after a predetermined number of wafer starts even if the performed processes did not erode the ring to the point where replacement would be necessary.
Due to the high price of consumable components, and to the high likelihood of underutilizing such parts, it is desirable to have the ability to accurately monitor the thickness of a consumable component during batch processing without stopping and/or opening the tool processing chamber. It would also be desirable to provide such monitoring ability in a simple and compact system that can be easily retrofitted to an existing processing system.